Scientists Discover Invisible Ecosystem Trapped Under Antarctic Ice

Roughly 2,000 miles south of New Zealand’s southernmost point lies Lake Enigma, an aptly named body of water tucked into coastal Antarctica. The lake’s ice cover is deeper than the lake itself: Although its liquid water is about 39 feet deep, 44 feet of ice sits on top, maintained by the region’s sub-freezing temperatures. But this icy, distant pool isn’t a wasteland. New research shows that a complex microbial ecosystem hides within Lake Enigma’s liquid depths, surprising scientists who once assumed it hosted very little life.

In a paper for Nature Communications Earth & Environment, researchers at the National Research Council of Italy (CNR) write that while other Antarctic lakes have received plenty of study, Lake Enigma has remained, well, an enigma. Many of the continent’s lakes are frozen top to bottom, making them uniquely interesting to geochemists and environmentalists. Others—including Lake Enigma—contain subzero water columns beneath their perennial ice covers, making them far more friendly to microscopic life forms. Understanding these lakes, the researchers write, is “foundational to understanding biology in Antarctica, a primarily microbial continent.”

During an Antarctic expedition that stretched between November 2019 and January 2020, researchers with the CNR drilled through Lake Enigma’s ice cover to retrieve samples of its water. Analyzing these samples led to two notable findings. First, the lake’s water column is “tightly isolated” from Earth’s atmosphere, making it difficult for most life to survive. Second (and despite this fact), Lake Enigma’s liquid layer is home to a large and phylogenetically diverse microbial ecosystem. 

RNA sequencing revealed 18 bacterial phyla and three single-celled eukaryotic phyla. About 60% of the microbes belonged to one of three bacterial phyla: Bacteroidota, Actinobacteriota, and Pseudomonadota. While Bacteroidota and Pseudomonadota exist virtually everywhere—not just in soil and seawater, but also in mammals’ guts and skin—Actinobacteriota are typically associated with soil health and plant growth here on land. 

Other “ultrasmall” bacteria belonging to the superphylum Patescibacteria made up less than a tenth of sampled microbes, but the fact that they existed at all was unexpected. Because they’re so small, these bacteria often lack the ability to synthesize amino acids, lipids, or other biologically necessary resources, making them dependent on microbes from other phyla. The fact that Patescibacteria are able to survive in Lake Enigma suggests that they are “working together” (AKA forming a symbiotic relationship) with other bacteria or preying on them directly, adding a layer of complexity to the lake’s invisible ecosystem that scientists didn’t expect.

“These bacteria have adopted an obligate symbiotic or predatory lifestyle, relying entirely on their respective prokaryotic host cells,” the researchers write. “The ultrasmall Patescibacteria…may play unusual roles in the lake’s ecosystem that do not play out in other ice-covered Antarctic lakes.

More research will be necessary to determine how Lake Enigma sustains its ecosystem despite its isolation and extreme conditions. Until then, the discovery of a diverse range of microbes under the lake’s frozen surface offers yet another nod to extremophiles: highly resilient organisms that could help scientists learn more about bioactive manufacturing, extraterrestrial agriculture, and even alien life.